The present invention relates generally to a pressure sensor and, more particularly, concerns a capacitive pressure sensor with a first capacitor pole element and at least one additional capacitor pole element, which are arranged at a distance from one another.
It is known to integrate pressure sensors in vehicle seats, for example, in order to detect whether the seat in question is occupied. This is relevant for the triggering of airbags, for instance.
Referring now to FIG. 1, it shows the base 11 of a seat. Placed on said base 11 is a pressure sensor 100 with electrical connecting lines 4 and 5. A seat cushion 9 is set on the base 11 and the pressure sensor 100.
During operation, a user generates a force F on the seat cushion 9 as a result of his body weight. The base 11 of the seat opposes this force so that the sensor 100 is squeezed and registers loading of the seat.
Known sensors have, as shown in FIG. 2, a first capacitor pole element 1 and a second capacitor pole element 3, which are composed of an electrically conductive material. The material used for this purpose may be a metal foil, for example.
The first capacitor pole element 1 and the second capacitor pole element 3 are separated from one another by an insulating device 2. The insulating device 2 consists of a compressible, electrically nonconductive material, and insulates the two capacitor pole elements 1, 3 from one another. The capacitor pole element 3 is connected to an electronic analysis unit (not shown) by the connecting line 5 of FIG. 1. The capacitor pole element 1 is connected to the connecting line 4 of FIG. 1 for this purpose.
When such a sensor is loaded by the weight of a person, this leads to compression of the insulating device 2 and thus causes the capacitor pole elements 1, 3 to approach one another. As a result, the capacitor comprising the capacitor pole elements 1, 3 changes its capacitance. When this change exceeds a predetermined threshold value, the electronic analysis unit recognizes this as a change from the unoccupied to the occupied state.
Removing the load from the seat causes the capacitor plates 1, 3 to move in the opposite direction, and brings about another change in capacitance which likewise can be detected. If the change is large enough, the seat is recognized as xe2x80x9cvacantxe2x80x9d again.
A disadvantage of the prior art is that the achievable functional reliability is inadequate. If the threshold value for the required change in capacitance is set too high, the weight of light individuals, such as children for instance, may under certain circumstances be insufficient for the seat to be recognized as occupied. If the required threshold value is set too low, material stresses in the seat, for instance resulting from changes in temperature and humidity, can cause a false xe2x80x9coccupiedxe2x80x9d signal.
It is thus an object of the present invention to provide a new and improved pressure sensor arrangement for vehicle seats.
According to the present invention, the foregoing and other objects and advantages are obtained by a pressure sensor comprising at least one capacitor pole element having at least one textured region on the surface of its conductive components facing toward the other capacitor pole element. The distance between the two capacitor pole elements is different in the textured region than in a region adjacent to the textured region. The difference between these two different distances can be changedxe2x80x94more particularly, reducedxe2x80x94by deformation of at least one capacitor pole element when the capacitor is subjected to pressure. This permits an increase in the capacitor""s capacitance as a result of concentration of conductive material of the capacitor pole element near the opposite capacitor pole element.
In another aspect of the invention, a pressure sensor with a first capacitor pole element, at least one additional capacitor pole element and at least one electrically nonconductive insulating device, of which at least part is arranged between the two capacitor pole elements is provided. Preferably, at least one capacitor pole element in at least one section of its surface facing the other capacitor pole element is spaced apart from the insulating device, and configured such that the section can be moved toward the insulating device through flexible deformation of the capacitor pole by subjecting the pressure sensor to pressure. This permits an increase in the capacitor""s capacitance as a result of concentration of conductive material of the capacitor pole element near the opposite capacitor pole element.
In another aspect of the invention, a pressure sensor with a first capacitor pole element, at least one additional capacitor pole element, and at least one electrically nonconductive insulating device, of which at least part is arranged between the two capacitor pole elements is provided. Preferably, at least one capacitor pole element on the surface of its electrically conductive components facing the other capacitor pole element has at least one textured region of a certain normal height. The normal height is capable of being reduced to a detection height through flexible deformation of the capacitor pole element when the pressure sensor is subjected to pressure.
In one embodiment of the invention, at least one of the capacitor pole elements is compressible toward the insulating device.
In another embodiment of the invention, one capacitor pole element is compressible only in one surface region facing the insulating device. This makes it possible to ensure sensor functionality while simultaneously making it possible to implement the capacitor pole element such that it is as robust as possible.
In another embodiment of the invention, one capacitor pole element is at least partly rigid and/or at least partly flexible.
In a further embodiment of the invention, one of the capacitor pole elements has a metallized textile made of synthetic fibers. This allows for economical manufacture and adequate flexibility of the capacitor pole element.
In still another embodiment of the invention, one of the capacitor pole elements has electrically conductive fibers, which are embedded in an electrically nonconductive, elastically deformable material. This allows for economical manufacture and adequate flexibility of the capacitor pole element.
In another embodiment of the invention, at least two different, electrically nonconductive media are arranged between the capacitor pole elements. At least one of the media is a fluid which can be displaced from the region between the two capacitor pole elements when pressure is applied to the pressure sensor. This makes it possible to use other media besides air, such as carbon dioxide or oil, for example, in order to avoid corrosion problems.
In further embodiments of the invention, the insulating device is at least partly rigid and/or at least partly flexible and/or is essentially incompressible in the direction of the applied pressure.
In another embodiment of the invention, the insulating device is embodied as a foil or film. This allows for a very flat construction.
In still another embodiment of the invention, the normal height of the texturing between the insulating device and the capacitor pole element, at least in one section, is between one and ten millimeters and, more particularly, between ten microns and one millimeter.
In another embodiment of the invention, a device for detecting the presence of a person on a motor vehicle seat has a pressure sensor with one of the above features.
In a further embodiment of the invention, the base of the motor vehicle seat constitutes one of the capacitor pole elements.